Water turbine



Dec. 13, 193s.

WATER TURBINE Filed July 17, 1957 A. JACKSON 2,140,230

Patented Dec. 13, 1938 UNITED STATES PATENT OFFICE WATER TURBINE Application July 17, 1937, Serial No. 154,313 In Great Britain January 1, 1937 2 Claims.

The present invention relates to improvements in axial flow impulse water turbines in which one or more jets of water are directed on to the runner at an angle with the plane of its revolution 5 from one or more nozzles.

In turbines of this type it has been usual for the centre line of the jet to enter the turbine runner on the centre line of the turbine runner, this centre line being a line in a plane of rotation of the runner and at right angles to the free jet path and passing through the runner axis and the axis of the jet. The point of intersection of the centre line of the runner and the jet axis is hereinafter called the intersection point.

With such known forms of turbine in order to obtain a reasonable degree of efficiency the ratio of maximum jet diameter to mean runner diameter was selected to be of the order of one to five.

An object of the present invention is to secure the highest possible ratio of maximum jet diameter to mean runner diameter whilst maintaining a desired degree of efficiency over a wide range of load, thus obtaining a relatively high specific speed with the use of one jet.

According to the present invention the centre stream line or axis of a jet intersects the surface of revolution of the entrance face of the runner at a point'spaced upstream from the intersection point by a distance equal to or greater than half the maximum jet diameter.

Alternatively this point may be disposed at a distance equal to or greater than one tenth of the mean diameter of the runner.

The invention is more particularly described with reference to the accompanying diagrammatic drawing in which- Figure 1 is a side elevation of the improved form of runner and jet disposition.

Figure 2, a corresponding plan view.

In axial flow impulse water turbines it has been usual for the jet disposition to be such that the centre line or axis of the jet intersected the surface of revolution of the entrance face of the runner at a point lying on the centre line of the runner. That is to say the conic section of jet with plane of the runner has been symmetrical to the runner centre line,

With a disposition of this type difficulties arise in obtaining a satisfactory control of the jet leaving the runner. The jet leaves the runner with its centre line at an excessive distance from the axis of the runner involving either an excessive number of vanes or excessively long vanes in the direction of flow of the water threads and consequential excessive frictional losses. Further, excessive rotation of the water stream or eddy currents occur due to rapid change in radius of the stream from the runner centre and to change of curvature of the runner vanes. 5

In the arrangement of the present invention as shown in Figures 1-2 the mean water thread travels along a path more or less evenly divided by a plane containing the intersection point L and the axis I-IJ of the runner, whereby the 10 mean change of radius of the water-thread is maintained relatively small and eddies and frictional losses reduced. As will be seen the centre stream line of the jet strikes the runner face at a point F upstream of the jet relative to the 15 intersection point and the jet leaves the runner at a point G where the distance G-H to the axis HJ of the runner is much shorter than the corresponding distance in the usual type of axial flow impulse water turbines. 20

It is now possible to reduce the number of vanes, or alternatively the length of the vanes in the direction of flow.

For usual jet ratios and angles and bucket depths, the condition above is approximately sat- 25 isfied if the mean water thread at entrance to the runner crosses the surface of revolution at a point such that if the runner vanes were removed the jet would have to travel a minimum of 6 of the mean runner diameter before it reached 30 its minimum distance from the axis of the runner.

Or from another point of view when the jet diameter is one fifth of the runner diameter the centre stream line or axis of the jet intersects the surface of revolution of the entrance face of the 35 runner at a point spaced upstream from the intersection point by a distance equal to or greater than half the maximum jet diameter.

The improvements due to the above have resulted in efficiencies of more than being 40 obtained with a ratio of maximum jet diameter to mean runner diameter of one to four and one eighth while with the jet entering on the intersection point and with a ratio of only one to four and one half the efficiency falls to only 73%. 45 The corresponding efliciency of the improved position is 81.5% while at reduced loads the emciency of the arrangement with the jet in the improved position is approximately 3% higher than with entrance on the intersection point. 50 The improvement in the capacity of the runner to deal efficiently with large jets is thus demonstrated and also the gain in efficiency due to smaller relative velocities.

The best speed of the type of runner described 55 is approximately the same as that for the same mean diameter Pelton runner, i. e. 40% to 50% of the jet Velocity.

The angle of AFH of the jet with the entrance plane of revolution of the runner is preferably about 20.

As seen from Figure 1 the conic section of the jet with the plane of the runner face is asymmetrical to the plane passing through the runner axis and the centre line of the runner and has its maximum area on the upstream side.

I declare that what I claim is:--

1. An axial flow impulse water turbine including a vaned runner and a jet disposed so that the centre streamline of the jet intersects the surface of revolution of the entrance face of the runner tersection point equal to or greater than half the maximum jet diameter, the ratio of the maximum jet diameter to the mean diameter of the runner being between one to four-and-an-eighth and one to four-and-a-half whereby to obtain a maximum turbine efficiency.

' ERNEST ALFRED JACKSON. 

